This invention relates generally to a track tension adjustment actuator and, more particularly, to an actuator operable to reduce tension on an idler wheel of endless track machine when the machine is traveling.
A tracked work machine, such as a track-type tractor or excavator, is typically supported and propelled by a pair of undercarriage assemblies. Each of the pair of undercarriage assemblies includes an endless track chain having a plurality of interconnected articulating components or links. Each undercarriage assembly typically also includes a drive wheel or sprocket and one or more idler wheels. The track chain is advanced around the drive wheel and the one or more idler wheels.
During operation of the work machine, it is necessary to maintain tension on the track chain in order to keep the chain from derailing or from jumping between teeth on the sprocket. In order to maintain tension on the track chain, a tension adjustment mechanism such as a hydraulic cylinder or coiled spring is often included in the undercarriage assembly.
With regard to excavators, it is generally desirable to have the track chain relatively taut during performance of a digging or other type of work operation in order to prevent the excavator from rolling back and forth within the interior of the track chain as a result of recoil forces generated during performance of the work operation. When digging with a tight track chain, the machine feels more stable to the operator and less wear occurs to the track components. To create tension on the track chain, the hydraulic cylinder or the coiled spring of the tension adjustment mechanism urges the idler wheel away from the drive wheel, increasing the dimension of the undercarriage assembly which the track chain must encircle.
In contrast, it is generally desirable to have the track chain relatively loose during advancement or travel of an excavator. By loosening or otherwise decreasing tension on the track chain below the tension used when digging, wear on the components associated with the undercarriage assembly is reduced. This increases the efficiency and even the useful life of the excavator. To reduce tension in the track chain, the hydraulic cylinder or coiled spring of the tension adjustment mechanism allows the idler wheel to move toward the drive wheel.
The tension adjustment mechanism also provides a recoil function in the track chain, accommodating temporary forces on the track such as when a rock or the like is ingested between the track and the wheels during advancement of the excavator. In these instances, the idler wheel is permitted to recoil toward the drive wheel in order to accommodate the extra length the track must encircle in order to accommodate the rock without breaking.
U.S. Patent No. 6,276,768 discloses a tensioning mechanism which decreases track tension when the machine is traveling. In an excavator embodiment, the ""768 patent provides a slave piston secured to the idler wheel and in fluid communication with a master piston. A pilot signal from any of the numerous components associated with the hydraulic drive system (or implement system) operates a valve assembly, which in turn controls the supply of fluid from the recoil accumulator to the master piston assembly. An increase in pressure from the hydraulic drive system causes the valve assembly to open the master piston assembly to tank, thereby allowing the slave piston to retract a predetermined amount and reduce track tension. A decrease in drive system pressure connects the master piston to the accumulator through the valve assembly, in turn extending the slave piston and increasing track tension. Use of the recoil accumulator fluid to adjust slack and increase tension to the track makes it difficult to adjust each parameter independently.
The present invention is directed to solving one or more of the problems or disadvantages set forth above of current work machines.
According to one aspect of the present invention, a track tensioning actuator is provided for a track assembly having, an idler wheel, a drive wheel, a drive track entrained about the drive wheel and idler, and a drive circuit operable to advance the drive wheel. The actuator comprises a hydraulic cylinder housing and a recoil piston positioned within the cylinder housing and coupled with the idler wheel. The cylinder housing and recoil piston form a recoil chamber pressurized to urge the recoil piston in a first direction away from the drive wheel. A travel piston is also positioned within the cylinder housing cooperating to define a travel chamber in fluid communication with the drive circuit. The travel piston is responsive to receipt of pressurized fluid from the drive circuit to contact and urge the recoil piston in a second direction away from the idler wheel. A track assembly using the actuator is also disclosed.
According to another aspect of the invention, a method is disclosed of tensioning a track assembly having an idler wheel, a drive wheel, a drive track entrained about the drive wheel and idler wheel, and a hydraulic motor operable to advance the drive wheel. The method comprises coupling a recoil piston of an actuator to the idler wheel, the actuator further including a cylinder housing, recoil chamber, a travel chamber, and a travel piston in fluid communication with the travel chamber. The recoil chamber is pressurized to tension the track. When pressurized fluid is supplied to the hydraulic motor to advance the drive wheel, pressurized fluid is responsively delivered to the travel chamber of the actuator, operating the travel piston to forcibly retract the recoil piston. Retraction of the recoil piston reduces the track tension during travel.